Factory production of the original Audi S4 (Typ 4A) began in August 1991 to serve as the performance version of the newly updated C4 platform 100 four-door, five-seat saloon. It was designed to replace the outgoing C3 based Audi 200 quattro turbo, which had been Audi's first true sports-saloon and had been discontinued at the end of 1990. Being the first S4 model from Audi, it is commonly referred to as the Ur-S4, derrived from the German: Ursprünglich augmentive word (meaning: original).

Audi mildly updated the C4-based model line in 1994 and dropped the 100 nomenclature; all variants of the former Audi 100 line were now re-badged as the Audi A6. In line with the switch in model name, Audi temporarily discontinued the use of the S4 name and began selling an updated but fundamentally identical version of the car, based on the "new" A6 and badged as S6. Despite the change in name, differences between the outgoing S4 and incoming S6 were primarily cosmetic.

A more powerful, more expensive and more exclusive variant known first as the S4 Plus and later as the S6 Plus was available from October 1992 through to July 1994.Built in very small numbers, the "Plus" models featured numerous performance enhancing upgrades; including the use of Audi's 4.2 litre V8 engine in place of the then current inline-five engine.

An all-new C5-based Audi A6 debuted for 1997, after which the S4 and S6 became distinctly separate models based on very different platforms.

The C4 variant S4 ended factory production after less than three years in July 1994.

C4 powertrain

In standard form, the powertrain detail of the C4-based S4 was available with only one engine, a single turbocharged and intercooled version of Audi's 2.2 litre 20-valve inline five cylinder engine This displaced 2,226 cubic centimetres (135.8 cu in) and was equipped with an advanced Bosch Motronic electronic engine control unit (ECU).This engine (parts code prefix: 034, identification code: AAN), developed a motive power output of 169 kilowatts (230 PS; 227 bhp) at 5,900 revolutions per minute (rpm) and 350 newton metres (258 lbf·ft) of torque 1,950 rpm. This powerplant made it rather powerful by contemporary standards, and the vehicle with five-speed manual transmission was able to accelerate from standstill to 100 kilometres per hour (62.1 mph) in just 6.2 seconds.

Both five- and six-speed manual transmissions (parts code prefix: 01E, identification codes: five-speed: CBD, CET, six-speed: CBL, CMG) were offered to European customers, but a five-speed manual was the only transmission available in North America; a four-speed automatic transmission (parts code prefix: 01F, identification code: CBF) was available as an option worldwide.Front and rear axle final drive ratio is either 4.111 or 3.889 (dependent on transmission type), and the rear axle (parts code prefix: 017, identification codes: AAT, AET) uses a driver-selectable electro-pneumatic-mechanical switchable diff lock.

Audi's quattro four-wheel-drive system was standard on the C4 S4/S6; a first-generation Torsen-based system which used the "T-1" automatically biasing centre differential (ATB) was used on vehicles equipped with manual transmissions, while a transfer box based system was used on vehicles equipped with an automatic transmission.

S4/S6 "Plus" models equipped with a 4.2 litre 206 kilowatts (280 PS; 276 bhp) all-aluminium alloy V8 engine (parts code prefix: 077, identification code: ABH) became available to European customers as an option from October 1992, only with the six-speed manual gearbox, in either saloon or Avant bodystyles.

C4 steering, brakes, wheels & tires

All C4 S4s' came equipped as standard with a conventional fixed-assistance rack and pinion power assisted steering (PAS) system. An electronically controlled 'servotronic' system, which varied the level of assistance in accordance with the road speed, was available as an option.

There were two different types of high performance brake systems on offer for the C4 S4. All S4s' initially had 310 millimetres (12.20 in) diameter by 25 millimetres (0.984 in) thick, radially ventilated disc brakes up front, each with an ATE single-piston sliding caliper inside a 'UFO' styled bell-shaped disc. With the introduction of the V8 engine, a new front brake setup became standard; again the discs used radial ventilation, but these front discs were now sized at 314 millimetres (12.36 in) by 30 millimetres (1.181 in) - with a conventionally mounted Lucas-Girling caliper in an external position over the disc. US models had smaller 276 millimetres (10.87 in) discs. The rear brakes, 269 millimetres (10.59 in) by 20 millimetres (0.787 in) and also radially ventilated - remained the same throughout C4 production; they used a Lucas-Girling single-piston sliding caliper with an integrated cable-actuated handbrake mechanism. A Bosch three-channel operation (four-channel sensing) Anti-lock Braking System (ABS) with a mechanical load sensing valve for the rear brakes was standard throughout production.

For roadwheel options, the standard five-arm "fuch" forged alloy wheels were 8.0Jx16H2 ET40, and were shod with 225/50 R16 sized tyres. Several other tyre and roadwheel designs were optionally available: a 7.5Jx15H2 ET40 six-spoke with 215/60 R15 tyres, a 8.0Jx16H2 ET40 five-double-spoke, a 7.5Jx16H2 ET35 six spoke "Avus", and a 8.0Jx17H2 ET40 ten-spoke.